1. Field of the Invention
The present invention relates to a transmission power control method and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Referring to FIG. 3, the mobile communication system, to which the “Enhanced Uplink” is applied, is explained.
In FIG. 3, the mobile station UE is establishing a radio link with only a cell #10 controlled by the radio base station Node B #1 (hereinafter, the cell which is controlled by the radio base station Node B is indicated as cell).
Here, in FIG. 3, an example that the mobile station UE in a Non-SHO state shifts to a SHO state where radio links with the cell #10 as well as a cell #20 are established is shown.
In such a case, the mobile station UE is configured to determine a transmission power of an “Enhanced Dedicated Physical Control Channel (E-DPCCH)”, based on a transmission power ratio between a transmission power of a “Dedicated Physical Channel (DPCH)” to which a closed loop transmission power control is performed and a transmission power of an E-DPCCH.
Here, the radio link includes the DPCH or an “Enhanced Dedicated Physical Channel (E-DPCH)” between the mobile station UE and the radio base station Node B.
In step S2001, the mobile station UE is establishing a data connection (E-DPDCH) for transmitting the uplink user data with the radio network controller RNC via the cell #10.
In step S2002, when the reception power of a common pilot channel from the cell #20 become more than or equal to the predetermined value, the mobile station UE transmits measurement report to the radio network controller RNC.
In step S2003, the radio network controller RNC requests the radio base station Node B #2 controlling the cell #20 to establish synchronization of radio links for uplink between the mobile station UE and the cell #20, based on the transmitted measurement report.
To be more specific, in step S2003, the radio network controller RNC transmits, to the radio base station Node B #2, a SHO setting request including SHO parameters. For example, the SHO parameters include a start time of the SHO.
In step S2004, the cell #20 transmits a SHO setting response for indicating that the cell #20 has received the SHO setting request.
In step S2005, the radio network controller RNC requests the mobile station UE to establish synchronization of radio links for downlink between the cell #20 and the mobile station UE.
To be more specific, in step S2005, the radio network controller RNC transmits, to the mobile station UE, a SHO setting request including the SHO parameters. In step S2006, the mobile station UE transmits a SHO setting response for indicating that the mobile station UE has received the SHO setting request.
The mobile station UE shifts from the Non-SHO state to the SHO state based on the SHO parameters. In step S2007, the mobile station becomes in the SHO state with the cell #10 and the cell #20.
Based on the above steps, the mobile station UE in the EUL is configured to connect to a plurality of cells simultaneously in the SHO state, so as to prevent the interruption of communication.
Here, with regard to a certain mobile station UE, a set of radio links established between the mobile station UE and the cell controlled by the radio base station Node B will be called as an “active set”.
The active set will be updated, for example, when the mobile station UE shifts between the Non-SHO state and the SHO state, or when the cells to which the mobile station UE establishes radio links are changed.
However, in the above method, when the active set is updated, the E-DPCCH transmission power offset, which is used to determine the transmission power required to receive, at the radio base station Node B, the E-DPCCH from the mobile station UE, will be drastically changed. Accordingly, the radio base station Node B cannot receive the E-DPCCH from the mobile station UE.
Further, there has been a problem that if the radio base station Node B cannot receive the E-DPCCH from the mobile station UE, the radio base station Node B cannot transmit ACK/NACK to the mobile station UE.
In such case, the probability of falsely detecting the ACK increases in the mobile station UE, and the probability that the mobile station UE transmits the subsequent uplink user data when it should have retransmitted the previous data increases. Accordingly, the data loss rate is increased, and the transmission efficiency will deteriorate drastically.